Many people are allergic to cats, dogs and other animals which trigger allergic rhinitis. Typical symptoms include sneezing, itchiness and a blocked or runny nose.
In the UK, pets are the second most important cause of allergy in the home, with 50% of children with asthma sensitised to the allergens of cats and 40% to dog allergens.
Allergic reactions are the result of the immune system overreacting to a perceived danger.
Normally the immune system identifies and responds to harmful viruses and bacteria, but in allergy the immune system wrongly identifies an allergen, such as pet dander, as dangerous and mounts an immune response.
In the case of cats, the most common cause of severe allergic reactions is a protein called Fel d 1 which is found in microscopic pieces of animal skin often accompanied by dried saliva from grooming.
The Cambridge team have discovered how this protein can trigger an inflammatory response when in the presence of a very common bacterial toxin found in the environment called lipopolysaccharide, or LPS.
Clare Bryant, who led the research at the University of Cambridge’s Department of Veterinary Medicine, says in a statement: "How cat dander causes such a severe allergic reaction in some people has long been a mystery. Not only did we find out that LPS exacerbates the immune response’s reaction to cat dander, we identified the part of immune system that recognises it, the receptor TLR4."
New pet allergy treatments
The scientists then used medication which inhibits the TLR4 response and found that it blocks the effects of the cat dander protein on human cells, thereby preventing an inflammatory response.
"As drugs have already been developed to inhibit the receptor TLR4, we are hopeful that our research will lead to new and improved treatments for cat and possibly dog allergy sufferers," Clare Bryant says.
The research was funded by the Wellcome Trust and the Medical Research Council and published in The Journal of Immunology.
'A big step forward'
Maureen Jenkins, director of clinical services at Allergy UK, describes the findings as "a big step forward in understanding how cat allergen causes such severe allergic reactions".
She continues in an emailed comment: "Cat allergen is particularly difficult to avoid as it is a 'sticky' molecule that is carried into every building on people's shoes and clothes. It can also still be found in a home, on the walls and ceiling or fittings, even a few years after a cat has ceased to live there.
"Therefore, this new information identifying the specific receptor interaction in the immune system could pave the way for treatments for those with persistent disease triggered by cat allergen and, in the future, potentially dog and house dust mite allergen."
Research News, University of Cambridge.
'Allergens as Immunomodulatory Proteins: The Cat Dander Protein Fel d 1 Enhances TLR Activation by Lipid Ligands', The Journal of Immunology.
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